3,3-bis-(indol-3-yl) phthalides



Aprilzs, 1970 CHAD-HAN LIN 3,509,173

' 5,3BIS(INDOL5-YL) PHTHALIDES Filed Jan. 30. 1967 FIG. I

SHEET OF RECORD MATERIAL COATED ON THE REAR WITH MINUTE PRESSURE-RUPTURABLE CAPSULES CONTAINING LIQUID SOLUTION OF CHROMOGENIC MATERIAL DEVELOPABLE ON CONTACT WITH AN ELECTRON- ACCEPTING MATERIAL OF THE LEWIS- ACID TYPE TO COLORED FORM.

RECEIVED SURFACE OF UNDERSHEET COATED WITH AN EIEPCTRON-ACCEPTING MATERIAL OF THE LEWIS-ACID FIG. Io-

INVENTOR CHAO'HAN LIN HIS ATTORNEYS United States Patent 3,509,173 3,3-BIS-(INDOL-3-YL) PHTHALIDES Chao-Han Lin, Dayton, Ohio, assignor to The National Cash Register Company, Dayton, Ohio, a corporation of Maryland Filed Jan. 30, 1967, Ser. No. 612,496 Int. Cl. C07d 27/56 US. Cl. 260326.14 2 Claims ABSTRACT OF THE DISCLOSURE A novel chromogenic material of normally colorless form, having a structural formula:

This invention pertains to novel chromogenic compounds for use in pressure sensitive record material and to an improved mark-forming manifold system incorporating these novel chromogenic compounds. More specifically, this invention pertains to 3,3-bis-(substituted indolyl) phthalides which have the form of substantially colorless, i.e. white, or slightly colored solids, or approach being colorless when in liquid solution, but which may be converted to dark-colored forms upon reactive contact with acidic material. As used in mark-forming systems, marking in desired areas on support webs or sheets may be accomplished by efiecting localized reactive contact between the chromogenic material and the acidic material on or in such a web or sheet, such material being brought thereto by transfer, or originally there in situ, the desired reactive contact forming dark-colored materials in the intended image areas.

Pressure-sensitive, mark-forming systems of the prior art include that disclosed in application for Letters Patent No. 392,404, filed Aug. 27, 1964, by Robert E. Miller and Paul S. Phillips, Jr., and now abandoned. The latter application provides a marking system of disposing on and/ or within sheet support material the unreacted markforming components (at least one of which is a polymeric 3,509,173 Patented Apr. 28, 1970 may be incorporated in a web or coated onto the surface of a web to provide a novel manifolding unit, and which are useful in carrying out improved methods of marking involving reactive contact with a color-activating material to develop dark-colored materials in areas where marking is desired.

It is another object of this invention to provide modified compounds, based upon the 3,3-bis-(substit-uted indolyl) phthalides, which are substantially colorless, or slightly colored offering a new and improved variety of chromogenic characteristics, and developing novel dark-colored substances upon contact with color-activating materials.

It is a further object of this invention to provide a new and improved mark-forming system which has the form of disposing within a web or upon the surface of a web or sheet support material unreacted chromogenic material which is capable of being reactively contacted with an acidic material to produce a dark-colored substance, thus providing marks having desirable color intensity and hue.

In accordancewith this invention, there are provided novel, substantially colorless or slightly colored, chromogenic compounds having the structural formula:

Where R and R consist of alkyl radicals having fewer than five carbon atoms, phenyl radicals, and hydrogen.

Examples of these novel compounds include: 3,3-bis- 1,2-dimethylindol-3-yl -phthalide.

3,3-bis- (2-ethylindol-3-yl) phthalide 3,3-bis- 1-methyl-2-phenylindol-3-yl) phthalide 3,3 -bisl-ethyl-2-methylindol-3 -yl) phthalide In accordance with another feature of this invention, a new composition of matter comprises the dark-colored substance having a resonant form developed by contact of a color-activating material with one of the abovementioned chromogenic compounds. The color-developing or -activating material is an acidic substance for converting the chromogenic compound to the resonant form.

The method of marking of this invention, i.e., by developing a dark-colored material from substantially colorless or slightly colored chromogenic compounds comprises providing a chromogenic compound selected from among the above-mentioned compounds and bringing such chromogenic compound into reactive contact in areas where marking is desired with an acidic coloractivating substance to produce a dark-colored resonant form of the chromogenic compound by the action thereon in said areas of the said acidic substance.

The acidic materials employed in this invention can be any compound within the definition of a Lewis acid, i.e., an electron acceptor. Preferably, acidic organic polymers such as phenolic polymers are employed as the acidic material. The novel chromogenic materials exhibit the advantage of improved color stability when reacted with such phenolic polymers. The solution formation of the solid particles of polymeric material in the same solvent with the substantially colorless chromogenic compounds allows penetration of the color into the support sheet, if porous, e.g., paper, so that the colored form of the chromogenic material sinks into the body of the sheet and is not merely on the surface of the sheet. This feature protects against erasure of recorded data by attrition of the surface of the record sheet.

Reference is to be taken to the drawings. FIGURE 1 is a diagrammatic representation of a two-sheet unit manifold, a perspective in which the bottom surface of the overlying is supplied on the surface or near it with a multiplicity of minute pressure-rupturable microcapsules, each containing a droplet. Each droplet contains a solution of the basic chromogenic component. An acidic component, such as an acid clay or a phenolic polymeric material lies Within the lower web or sheet or upon the upper surface of the lower web or sheet. A colored mark is made by the use of a stylus, type character, or other pressure-writing means applied to the two-sheet unit manifold.

The encapsulated droplets are released on the rupture of the capsules in writing operations, as shown in FIG- URE 1a. The liquid of the released droplets is transferred in the pattern of the data configuration to the top of the underlying sheet. The top of the underlying sheet is coated or impregnated with a material reactant with the chromogenic material, e.g., a phenolic polymer material having an acid-reacting OH group. The drawings show capsules on the oversheet containing a liquid solution of chromogenic material. However, the capsules can contain the polymeric phenolic material in liquid solution and the top surface of the under-sheet may be supplied with the chromogenic material in particulate form. The im-. provement in the system is the chromogenic compound which is the novel substance of the instance invention.

Referring again to FIGURE 1 comprising an upper web or sheet having the chromogenic material dispersed within or upon in a contiguous juxtaposition, it is possible to incorporate the chromogenic material in a solid, crystalline-state in a binder material so that the chromogenic material may be transferred from the upper web or sheet upon the application of pressure from a stylus 4 to deposit some of the chromogenic material on a surface carrying a color activating polymeric material. Preferably, the chromogenic substance is dissolved in a solvent and minute droplets of the solution of the chromogenic material are encapsulated in minute, pressure-rupturable capsules. Obviously, many other arrangements, configurations and relationships of the solvent and the markforming materials, with respect to their encapsulation and location on the support sheet or webs can be envisioned. Such arrangements are thoroughly described in the aforementioned application Ser. .No. 392,404 to Miller et al., and need not be repeated herein.

It is noted that the polymeric mark-forming components should have a common solubility with the chromogenie material in at least one liquid solvent when the acid-reacting material is a phenolic or other organic acidic polymer. It is also noted that in a single system several chromogenic materials may be used with the same or different polymeric materials. Several polymeric materials can be reactively contacted with a single chromogenic compound or with a mixture of chromogenic compounds.

As mentioned above, the solvent is maintained in physical isolation in minute droplets until such time as it is released by application of pressure. This may be accomplished by several known techniques, but preferably isolation is maintained by individual encapsulation of the solvent droplets in a microcapsule according to the procedures described, for example, in US. Patent No. 2,712,507, issued to Barrett K. Green on July 5, 1955; 2,730,457 issued to Barrett K. Green and Lowell Schleicher on Jan. 10, 1956; 2,800,457 issued to Barrett K. Green and Lowell Schleicher on July 23, 1957; and 2,800,458 issued to Barrett K. Green on July 23, 1957, reissued as Reissue Patent No. 24,899 on Nov. 29, 1960. The microscopic capsules, when disposed within or upon a supporting web as a multiplicity in contiguous juxtaposition, are rupturable by pressure, such as normal marking pressures utilized, for example, in writing or typing operations.

The material or materials chosen as the wall material of the microcapsule, in addition to being pressure rupturable, must be inert or unreactive with respect to the contents of the capsule and the other mark-forming components so that the wall material remains intact under normal storage conditions until such time as it is released by the application of marking pressure. Examples of such wall materials are gelatin, gum arabic and many others thoroughly described in the aforementioned patents.

For use in record material, the capsule size should not exceed 50 microns in diameter. Preferably, the capsules should be smaller than 15 microns in diameter.

The acidic organic polymeric material useful in this invention include phenol aldehyde polymers, phenol acetylene polymers, maleic acid-rosin resins, partially or wholly hydrolyzed styrene-maleic anhydride copolymers and ethylene-maleic anhydride copolymers, carboxy polymethylene and wholly or partially hydrolyzed vinyl methyl ether maleic anhydride copolymer and mixtures thereof.

Among the phenolic polymers found useful are alkylphenol-acetylene resins, which are soluble in common organic solvents and possess permanent fusibility in the absence of being treated by cross-linking materials. A specific group of useful phenol-aldehyde polymers are members of the type commonly referred to as novolacs (as sold by Union Carbide Corp., New York, N.Y.) which are characterized by solubility in common organic solvents and which are, in the absence of cross-linking agents, permanently fusible. Generally, the phenolic polymer material found useful in practicing this invention is characterized by the presence of free hydroxyl groups and the absence of groups such as methylol, Which tend to promote infusibility or cross-linking of the polymer, and by their solubility in organic solvents and relative insolubility in aqueous media. Again, obviously, mixtures of acidic materials can be employed.

Resoles, if they are still soluble, may be used, though subject to change in properties upon aging.

A laboratory method useful in the selection of suitable phenolic resins is the determination of the infra-red absorption pattern. It has been found that phenolic resins showing an absorption in the3200-3500 cm.- region (which is indicative of the free hydroxyl groups) and not having an absorption in the 1600-1700 cm. region are suitable. The latter absorption region is indicative of the desensitization of the hydroxyl groups and, consequently, makes such groups unavailable for reaction with the chromogenic materials.

The preparation of the phenolic formaldehyde polymeric materials for practicing this invention is described in Industrial and Engineering Chemistry, vol. 43, pp. 134-141, January 1951, and a particular polymer thereof is described in Example 1 of U.S. Patent No. 2,052,093, issued to Herbert Honel on Aug. 25, 1936, and the preparation of the phenolacetylene polymers is described in Industrial and Engineering Chemistry, vol. 41, pp. 73-77, January 1949.

The preparation of the maleic anhydride copolymers is described in the literature, such as, for example, one of the maleic anhydride vinyl copolymers, as disclosed in the publication, Vinyl and Related Polymers, by Calvin E. Schildknecht, second printing, published April l959, by John Wiley & Sons, Incorporated. See pp. 65-68 (styrene-maleic anhydride copolymer), 628-630 (vinyl methyl ether-maleic anhydride copolymer), and 530-531 (ethylene-maleic anhydride copolymer).

When the acidic material is one of the aforementioned organic polymers, the liquid solvent chosen must be capable of dissolving the mark-forming components. The solvent may be volatile or non-volatile, and a smgle or multiple component solvent may be used which is wholly or partially volatile. Examples of volatile solvents useful in the fore-described basic chromogen-acidic polym r are toluene, petroleum distillate, perchloroethylene, and xylene. Examples of non-volatile solvents are high-boiling point petroleum fractions and chlorinated biphenyls.

Generally, the solvent chosen should be capable of d1ssolving at least 0.3%, on a weight basis, of the chromogenic material, and about a 35%, on a weight basis, of the polymeric material to form an efiicient reaction. However, in the preferred system, the solvent should be capable of dissolving an excess of the polymeric material, so as to provide every opportunity for utilization of the chromogenic material and, thus, to assure the maximum coloration at a reaction site.

A further criterion of the solvent is that it must not interfere with the mark-forming reaction. In some nstances, the presence of the solvent may interfere with the mark-forming reaction or diminish the intensity of the mark, in which case the solvent chosen should be sufficiently vaporizable to assure its removal from the reaction site after having, through solution, brought the mark-forming components into intimate admixture, so that the mark-forming contact proceeds.

Since the mark-forming reaction requires an intimate mixture of the components to be brought about through solution of said components, one or more of the markforming components may be dissolved in the isolated solvent droplets, the only requirement being that at least one of the components essential to the mark-forming reaction be maintained isolated until reactively contacted with the other.

In the usual case, the mark-forming components are so chosen as to produce a mark upon application of pressure at room temperature (20 to 25 degrees centigrade). However, the present invention includes a system in which the solvent component is not liquid at temperatures around room t mperature but is liquid and in condition for forming solutions only at elevated temperatures.

The support member on which the components of the system are disposed may comprise a single or dual sheet assembly. In the case where all components are disposed on a single sheet, the record material is referred to as a self-contained system. Where there must be a migration of the solvent, with or without mark-forming component, from one sheet to another, the record material is referred to as a transfer system. (Such a system may also be referred to as a two-fold system, in that at least two sheets are required and each sheet includes a component, or components, essential to the mark-forming reaction.) Where a copious amount of the colored reaction product in liquid form is produced on a surface of one sheet, it may produce a mark by transfer to a second sheet as a colored mark.

In the preferred case, where microcapsules are employed, they may be present in the support material either disposed therethroughout or as a coating thereon, or both. The capsules may be applied to the sheet material while still dispersed in the liquid vehicle in which they were manufactured, or, if desired, separated and the separated capsules thereafter dispersed in a solution of the polymeric component (for instance, 30 grams of water and 53 grams of a 1% aqueous solution of polyvinyl methyl ether maleic anhydride) to form a coating composition in which, because of the inertness of the solution and the capsules, both retain their identity and physical integrity. When this composition is disposed as a film on the support material and dried, the capsules are held therein subject to rupture to release the liquid contained. This latter technique, relying on the inertness of the microcapsule and the dispersing medium of the filmforming mark-forming component, allows for a method of preparing a sensitive record coating with the capsules interspersed directly in a dry film of the polymeric material as it is laid down from the solution. A further alternative is to disperse in a liquid medium one or more mark-forming components, insoluble therein, and disperse in said medium the insoluble microcapsules, with the result that all components of the mark-forming system may be disposed on or within the support sheet in the one operation. Obviously, the several components may be applied individually.

The respective amounts of the several components will vary, depending primarily upon the nature of the materials and the architecture of the record material unit. Suitable lower amounts include, in the case of the chromogenic material, about .005 to .075 pound per ream (a ream in this application meaning five hundred (500) sheets of 25" x 38" paper, totaling 3,300 square feet); in the case of the solvent, about 1 to 3 pounds per ream; and in the case of the polymer, about /2 pound per ream. In all instances, the upper limit is primarily a matter of economic consideration.

In the instance where the mark-forming components are interspersed throughout asingle support sheet material (so-called self-contained unit), the following technique or procedure has been found useful:

The slurry of capsules may be applied to a wet web of paper as it exists on the screen of a Fourdrinier paper machine, so as to sink into the paper web a distance depending on the freeness of the pulp and the water content of the Web at the point of application.

The capsules may be placed directly in the paper or in a support sheet. Not only capsule structures, but films which hold a multitude of droplets for local release in an area subject to pressure may be utilized. (See U.S. Patent No. 2,299,694, which issued Oct. 20, 1942, to B. K. Green.)

With respect to the acidic organic polymeric component, a solution thereof in an evaporable solvent is introduced into twice as much water and agitated while the evaporable solvent is blown off by an air blast. This leaves an aqueous collodial dispersion slurry of the polymeric material, which may be applied to the paper so as to leave a surface residue, or the slurry may be applied to paper at the size-press station of a paper-making machine by roller. In another method of making a polymer-sensitized sheet, the Water-insoluble polymer is ground to the desired particle size in a ball mill with water, preferably with a dispersing agent, such as a small quantity of sodium silicate. If a binder material of .hydrophilic properties is ground with the phenolic material, the binder itself may act as a dispersant. If desired, an amount of binder material of up to 40%, by weight, of the employed amount of the polymeric material may be added to the ball-milled slurry of materials, such binder materials being of the paper coating binder class, including gum arabic, casein, hydroxyethylcellulose, and latex (such as styrene-butadiene copolymer). If desired, oil adsorbents in the form of fullers earths may be added to the polymeric material particles to assist in retaining, in situ, the liquid droplets to be transferred to it in data-representing configuration, for the purpose of preventing bleeding of the print.

Another way of applying the chromogenic or polymeric material individually to a single sheet of paper is by immersing a sheet of paper in a 1% to 10% solution of the material in an evaporable solvent. Obviously, this must be done alone for each reactant, because if the other reactant material were present, it would result in a premature coloration over the sheet area. A dried sheet with one component then may be coated with a solution of the other Component, the solvent of which is a non-solvent to the already supplied component.

The polymeric material may be dissolved in ink composition vehicles to form a printing ink of colorless character and, thus, may be used to spot-print a proposed record sheet unit sensitized for recording in a reactionproduced color in those areas by application of a solution of the chromogenic material.

In the case of phenolic polymer, a printing ink may be made of up to 75% weight, of the phenolic polymeric material in a petroleum solvent to a viscosity suitable for printing purposes. The relative amounts of compoments to be used are the most convenient and economical amounts consistent with proper visibility of the recorded data. The resolution of the recorded data is, among other things, dependent on particle size, distribution and amount of particles, liquid solvent migration, chemical reaction efliciency, and other factors, all of which are things that may be worked out empirically by one familiar with the art, and which do not determine the principle of the invention, which, in part, involves means for enabling the bringing into solution, by marking pressure, of two normally solid components in a common liquid solvent component held isolated as liquid droplets, preferably in marking-pressure-rupturable capsules having film walls, or else held isolated in a continuous marking-pressure-rupturable film as a discontinuous phase.

In the base-acid color system of this invention the acidic mark-forming component(s) reacts with the basic chromogenic material( s) to effect distinctive color formation or color change. In a multisheet system in which an acidic organic polymer is employed, it is desirable to include other materials to supplement the reactants. For example, kaolin can be added to improve the transfer of the liquid and/or the dissolved materials between the sheets. In addition, other materials such as bentonite, attapulgite, talc, feldspar, halloysite, magnesium trisilicate, silica gel, pyrophyllite, zinc sulfate, zinc sulfide, calcium sulfate, calcium citrate, calcium phosphate, calcium fluoride, barium sulfate and tannic acid can be included.

Various methods known to the prior art and disclosed in the aforementioned application Ser. No. 392,404 to Miller et al., and US. patent application Ser. No. 420,193 to Phillips et al., now US. Patent No. 3,455,721 can be employed in coating compositions of the mark-forming materials into their supporting sheets. An example of the compositions which can be coated onto the surface a 1 of an underlying sheet of a two-sheet system to react with the capsule coating on the underside of an overlying sheet is as follows.

Coating composition: Percent by weight Phenolic polymer mixture 17 Paper coating kaolin (white) 57 Calcium carbonate 12 Styrene butadiene latex 4 Ethylated starch 8 Gum arabic 2 EXAMPLE I Preparation of 3,3-bis-(1,2-dimethylindol-3-yl)-phthalide To a mixture of 15.0 grams of 1,2-dimethylindole, 7.5 grams of phthalic' anhydride and 40 milliliters of benzene under ice-cooling was gradually added 16.0 grams of anhydrous aluminum chloride. After being stirred at 5-10 C. for 20 minutes and at room temperature for 4 hours, the reaction mixture was extracted with ethyl ether, and decomposed with dilute hydrochloric acid. The precipitate was purified and finally recrystallized from ethanol. The intermediate 1,2-dimethy1-3-(2 carboxy benzoyl) indole, melting at 238-239 was obtained.

0.15 gram of the intermediate prepared above, 0.15 gram of 1,2-dimethylindole, and 5 milliliters of acetic anhydride were mixed and refluxed for 30 minutes. 10 milliliters of water was added and the mixture then evaporated to dryness. A sufiicient quantity of benzene to solubilize the dry solid was added. The benzene solution was extracted with a 10% sodium carbonate solution, washed with water, dried with sodium sulfate, concentrated to approximately 5 milliliters, and thereafter cooled. A solid exhibiting a weight of milligrams was dissolved in 10 milliliters of benzene and treated with 10 milliliters of petroleum ether, and the resulting mixture filtered. The filtrate upon standing yielded the pure phthalide exhibiting a weight of 45 milligrams and a melting point of above 300 C. A benzene solution of the product turned red when contacted with attapulgite clay coated on paper and when contacted with phenolic polymer coated on paper.

EXAMPLE II Preparation of 3,3-bis-(2-phenylindol-3-yl) phthalide 5.8 grams of Z-phenylindole, 4.4 grams of phthalic anhydride, and 25 milliliters of benzene were stirred in a milliliter flask immersed in an ice-bath. 8.8 grams of aluminum chloride was slowly added during a time interval of 5 minutes. The mixture was stirred at the temperature of the ice-bath for 30 minutes, at room temperature for 30 minutes, and at 50 C. for 30 minutes. 100 milliliters of 3 normal hydrochloric acid was added to the reaction mixture to decompose the aluminum previously formed. A purple solid precipitated from solution; the solid was washed with water and treated with milliliters of dilute ammonium hydroxide. Material insoluble in the ammonium hydroxide solution was discarded. The solution was then treated with activated charcoal, made acid by the addition of dilute hydrochloric acid solution until the pH was adjusted to 2. A solid which precipitated from solution was stirred with 100 milliliters of water for 30 minutes. The solid, when dried in air, exhibited a weight of 4.3 grams. The solid was then boiled in 200 milliliters of benzene. A part of the solid not soluble in benzene was dissolved in 50 milliliters of denatured alcohol. Upon the addition of petroleum ether, the intermediate product crystallized from solution. The intermediate exhibited a weight of 3.7 grams.

1.7 grams of the intermediate prepared above, 1.0 gram of 2-phenylindoie, and 20 milliliters of acetic anhydride were heated in a 50 milliliter beaker on a hot plate to a temperature slightly below the boiling point for 20 minutes. The mixture was poured into 100 milliliters of water, and made alkaline with ammonium hydroxide. A purple solid precipitated from solution. The solid precipitate was boiled in 120 milliliters of benzene and a small quantity of activated charcoal. Upon standing, a white solid, exhibiting a weight of 0.5 gram precipitated from a pale yellow solution. The solid precipitate upon recrystallization from a benzene solution exhibited a weight of 0.4 gram, and a melting point of 212. A benzene solution of the product turned a dark blue-gray color when contact with attapulgite clay coated on paper, and a light blue-gray color when contacted with a phenolic polymer coated on paper.

EXAMPLE III Preparation of 3,3-bis-(2-ethylindol-3-yl) phthalide 1.45 grams of Z-ethylindole, 1.48 grams of phthalic anhydride and a trace amount of anhydrous zinc chloride were heated together for 45 minutes. The reaction mixture was boiled with 75 milliliters of water and filtered. After washing with hot water and benzene, the precipitate was recrystallized from ethanol. The intermediate, 2-ethy1- 3-(2-carboxybenzoyl) indole, thus formed, exhibited a weight of 1.6 grams and a melting point of 2l0211 C.

1.47 grams of the intermediate prepared above, 0.73 gram of Z-ethylindole, and 15 milliliters of acetic anhydride were heated together for 15 minutes. The reaction mixture was poured into 100 milliliters of water, made alkaline with ammonium hydroxide, stirred for 120 minutes and filtered. The crude product, weighing 2.2 grams, was recrystallized from benzene to yield a pure 3,3-bis-(2-ethylindol-3-yl) phthalide, melting at 223-225 C. A benzene solution of the product turned a red color when contacted with attapulgite clay coated on paper or with a phenolic resin coated on paper.

EXAMPLE 1V Preparation of 3,3-bis-(l-methyl-Z-phenylindol- 3-yl) phthalide 4.5 grams of I-methyl-Z-phenylindole, 3.0 grams of phthalic anhydride, and 30 milliliters of benzene were stirred in a flask under ice-cooling. To the mixture was slowly added 5.9 grams of anhydrous aluminum chloride.

10 The mixture was stirred at 510 C. for 30 minutes and at room temperature for 4 hours; decomposed with 3 normal hydrochloric acid, and the precipitate filtered. A crude product was puified and finally recrystallized from ethanol. The pure intermediate I-meth-yl-Z-phenyl- 3-(2-carboxybenzoyl) indole melted at 215-216 C.

0.71 gram of the intermediate, prepared above, 0.41 gram of l-methyl-Z-phenylindole and 15 milliliters of acetic anhydride were heated together for 15 minutes, poured into milliliters of water, made alkaline with ammonium hydroxide, and stirred for 120 minutes. The precipitate was separated, purified, and finally recrystallized from ethanol. The product 3,3-bis-(1-methyl-2- phenylindol-S-yl) phthalide melted at 215217 C. A benzene solution of the said phthalide turned a purple color when contacted with attapulgite clay coated on paper or with phenolic resin coated on paper.

EXAMPLE V Preparation of 3,3-bis-(1-ethyl-2-methylindol- 3-yl) phthalide 1.54 grams of 1-ethyl-2-methyl-3-(2-carboxybenz0yl) indole, 0.8 gram of 1-ethyl-2-methylindole and 5 milliliters of acetic anhydride were placed in a 50 milliliter flask immersed in a waterbath maintained at 28-32 C. for 5 hours. The precipitate formed was filtered, washed with ethyl ether, and purified. The product 3,3-bis-(1- ethyl-2-methylindol-3-y1) phthalide, melted at 225-227" C. A benzene solution of the said phthalide turned a red color when contacted with attapulgite clay coated on paper or with phenolic resin coated on paper.

What is claimed is:

1. 3,3-bis-(-phenylindol-3-yl) phthalide.

2. 3,3-bis-(1-methyl-2-phenylindol-3-yl) phthalide.

References Cited Oddo: Chem. Abs., vol 19, p. 2823 (1925).

ALEX MAZEL, Primary Examiner J. A. NARCAVAGE, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,509,173 Dated April 28, 1970 Inventor(s) Chao-Han Lin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 27, "was obtained" should be --was thus obtained--. Column 9, line 12, "contact" should be --contacted-- Column 10, line 4, "puified" should be -purified-- Claim 1,

"3, 3-bis-(-phenylindol-" should be 3, 3-bis-(2-phenylindo1- oli.....\.;u Am "12 JD u-r LL mus m ymilLFlmhqi- MOI:-

X-ll9l-67 2-13-70 NCR 

